The present disclosure relates to aircraft environmental control systems. More specifically, the present disclosure relates to a method of installing a diffuser in an air cycle machine.
Air cycle machines are used in environmental control systems in aircraft to condition air for delivery to an aircraft cabin. Conditioned air is air at a temperature, pressure, and humidity desirable for aircraft passenger comfort and safety. At or near ground level, the ambient air temperature and/or humidity is often sufficiently high that the air must be cooled as part of the conditioning process before being delivered to the aircraft cabin. At flight altitude, ambient air is often far cooler than desired, but at such a low pressure that it must be compressed to an acceptable pressure as part of the conditioning process. Compressing ambient air at flight altitude heats the resulting pressurized air sufficiently that it must be cooled, even if the initial ambient air temperature is very low. Thus, under most conditions, heat must be removed from air by the air cycle machine before the air is delivered to the aircraft cabin.
Air cycle machines typically include rotating parts connected to a rotating shaft that extends through static parts of the air cycle machine. Each end of the rotating shaft is supported with a journal bearing to mount the rotating shaft in the static parts of the air cycle machine. During assembly of the air cycle machine, the static parts need to be closely aligned with one another so that the journal bearings on either end of the air cycle machine can also be closely aligned. It is important to closely align the journal bearings so the rotating shaft rotates about an axis through the center of the rotating shaft. Any misalignment between the journal bearings can cause rubbing and wear between the rotating parts and the static parts.
To closely align the static parts, two processes can be undertaken. First, prior to assembly of the entire air cycle machine, the static parts can be pinned together. The pinning process includes assembling and aligning the static parts, drilling a hole though adjacent static parts, and placing a pin in the drilled holes. The static parts can then be disassembled and reassembled with all of the air cycle machine parts. The pins act as guides to ensure the static parts are properly aligned. The pinning process adds additional complexity to the assembly process, as it creates more components in the air cycle machine. The second option to ensure the parts are closely aligned is to precision manufacture the static parts so that they can be perfectly aligned during assembly of the air cycle machine. Precision manufacturing can be costly and time consuming.